Homovanillic acid (HVA) levels of 12 discrete rat brain areas were determined by a mass fragmentographic method using the reaction gas chromatographic technique. The use of reaction gas chromatography increased the sensitivity for determination of HVA. The sensitivity of this method allows measurement of HVA in small amounts of brain tissue. The HVA levels in polar, medial, and lateral fields of prefrontal cortex, anterior cingulate cortex, septum, amygdala, A12, A13, and A14 dopaminergic neurons were 0.417 +/- 0.018 ng/mg protein, 0.689 +/- 0.004, 0.753 +/- 0.024, 0.496 +/- 0.029, 1.311 +/- 0.046, 0.555 +/- 0.008, 1.949 +/- 0.077, 1.109 +/- 0.112, and 0.489 +/- 0.019, respectively. The HVA levels in these areas are first reported in the present paper.